Dumbbell



FIG. 1 is a perspective view of a dumbbell of my design;

FIG. 2 is a top plan view thereof, with the bottom plan view, front elevational view and rear elevational view being the same; and,

FIG. 3 is right end elevational view thereof, with the left end elevational view being the same. 

The ornamental design for a dumbbell, as shown and described. 